Apparatus for the electrostatic atomization of liquids



Oct. 22, 1968 w. slMM APPARATUS FOR THE ELECTROSTATIC ATOMIZATION OF LIQUIDS Filed Feb. 28, 1967 INVENTOR.

WALTER IMM United States Patent 3,406,660 APPARATUS FOR THE ELECTROSTATIC ATOMIZATION 0F LIQUIDS Walter Simm, Leverkusen, Germany, ass'ignor to Agfa- Gevaert Aktiengesellschaft, Leverkusen, Germany, a corporation of Germany Filed Feb. 28, 1967, Ser. No. 619,415

Claims priority, application Germany, Mar. 18, 1966, A 51,884 5 Claims. (Cl. 118-626) ABSTRACT OF THE DISCLOSURE Apparatus for developing electrophotographic charge images includes using a ring-shaped or annular electrode which is rotated to electrostatically atomize the liquids which are received by an electrophotographic charge image. The electrode may be mounted upon guide rollers which are disposed in a housing.

This invention relates to an apparatus for the electrostatic fine-atomization of liquids, particularly for the development of electrophotographic charge images.

According to conventional electrostatic atomization processes, liquids can be electrostatically atomized by bringing them on to the surface of electrodes which produce a strong, non-uniform electric field in the area surrounding them when a sufficiently high potential is applied.

Conventional electrode designs include, for example, metal cylinders widened in the form of a funnel at the spraying end, bell-shaped electrodes, split nozzles, spraying edges, rotating discs, bristles and filaments or wires with wettable surfaces. The electrode designs are adapted both to the particular purpose for which the electrodes are to be used, and to the working conditions. For example, bell-shaped electrodes, spraying edges or rotating discs are frequently used for paint spraying. Their surfaces or spraying edges are continuously supplied with the liquid to be atomized. In this way, an electrically charged paint mist is obtained which is deposited on a workpiece which forms the counter-electrode.

Electrodes which develop extremely high field intensities in the area surrounding them even when low potentials are applied, are suitable for the fine atomization of relatively small quantities of fairly conductive liquids such as are used, for example, as developer liquids in electrophotography. Such electrodes include thin tubes with a sharp spraying edge, bristles, wires and filaments. In addition, the liquids have to be supplied in carefully controlled quantities to those points along the electrode at which atomization takes place, in order to prevent the formation of relatively large drops. One practical embodiment of a tube electrode whose spraying edge is continuously wetted, is described in German patent specification No. 1,202,639. In this device, the liquid is pumped from a supply container through a screw conveyor inside a rotating cylinder to the spraying edge, the excess being returned to the supply container through an overflow pipe. The spraying edge is wetted with the liquid and atomization can take place when a suitably high potential is applied to the electrode. This arrangement has the disadvantage that the spraying liquid is deposited in the form of a circle or ring on a fiat counterelectrode with the result that there is an unspraying zone in the middle of the spraying surface. Since, however, the aerosol has usually to be homogeneously deposited, this spraying apparatus has to be additionally moved parallel to the sprayed surface. The machinery required for this purpose is relatively expensive. In addition, correct wetting of the spraying edge involves exact posi- 3,406,660 Patented Oct. 22, 1968 ice tioning of the return flow pipe, the setting being different for different types of liquids. Some liquids do not wet the metal edge sufficiently and detrimentally affect the reliability of the performance of the atomization electrode. Even where bristles and filament electrodes are used, difficulties are encountered in continuous operation because the necessary wetting and driving means are missing.

The object of the present invention is to obviate the disadvantages referred to above and to provide a simple means of electrostatically atomizing liquids with extreme fineness, so that the electrically charged aerosol can be uniformly deposited on a flat counter-electrode.

It has now found that the fine atomization of liquids with an annular atomization electrode affords surprising advantages.

FIG. 1 is a side elevation view of a schematic representation of one embodiment of this invention;

FIG. 2 is an end elevation view of the embodiment of the invention shown in FIG. 1;

FIG. 3 is an elevation view similar to FIG. 1 of a modified form of this invention;

FIG. 4 is a side elevation vie-w of still another embodiment of this invention;

FIG. 4a is an end elevation partly in section of the embodiment of the invention shown in FIG. 4.

According to the invention, the apparatus comprises an annular electrode 1 which is mounted on at least three guide rollers, 2, 3 and 4, and which is rotated about an axis perpendicular to the plane of the ring or annulus, by a driving motor 5, an insulating shaft 6 and the guide rollers. Metal can be used as the electrode material, although it is possible to use a non-conductor with relatively conductive liquids. The ring is preferably from 0.2 to 3 mm. thick, whilst its diameter is optional, depending upon the stability of the electrode material. The ring can be rotated at speeds of, for example, 10 to 60 rpm. The guide rollers 2, 3 and 4 and part of the ring 1 are accommodated in a metal housing 7 which acts as a supply container for the liquid 8 to be atomized, and at the same time prevents it from evaporating. The ring 1 dips into the liquid and, in doing so, takes up the liquid on its surface. As it continues to rotate, the ring gives up some of the liquid to the roller 4 and on leaving the container, the ring 1 retains a film of liquid. The container 7 is connected to a high tension source 9, thus receiving the negative or positive potential required for atomization, which is transferredto the ring leading to atomization of the liquid. Arranged above the ring is an earthed counter-electrode 10 in the form of a plate. During atomization, several spray globules 16 are formed at short intervals over the exposed part of the ring 1, from which the liquid is converted into ultra-fine aerosol. If a suitable dye solution is used as the liquid, for example Ceresschwarz BN (C.I. No. 26150) in benzyl alcohol, which has a specific resistance of 1.10 ohm cm, a uniformly dyed surface is obtained on the counterelectrode 10, its area being governed both by the electrode gap and by the potential applied.

FIGURE 3 shows a different way of mounting the ring. In this instance, the liquid is applied by a roller 11 to the ring 1, which is held by driving rollers 12 and 13 and which does not itself dip into the bath.

In contrast to the conventional disc or plate electrodes it is possible, by using a ring electrode, to obtain a much more favorable atomization effect and to scatter the aerosol produced over a wider area, because the electric field can develop more fully in the area surrounding the exposed part of the ring than it can on the edge of a disc. Only a narrow zone on the counter-electrode is sprayed when a rotating disc is used as the atomization electrode,

whereas the aerosol is deposited over an extensive area when an annular electrode is used. In addition, the annular form has the advantage that the quantity of liquid adhering to the relatively small surface of the ring, for example a ring of wire 1 mm. in diameter, can only be atomized from the area immediately surrounding a spray globule, with the result that fairly large drops cannot be formed.

As already known, ultra-fine atomization is obtained with liquids of relatively high conductivity, for example in the range from 10- to ohm cm. It is known from German specification A 50,511 that liquids of this kind having negative potential can only be effectively atomized when the electrode is surrounded by a gas whose dielectric strength is considerably higher than that of air. An example of one such gas i dichlorodifluoromethane. For atomization under these conditions, the apparatus according to the invention can be accommodated in a vessel filled with the aforementioned gas. Another more simple method of supplying the gas are shown in FIG- URES 4 and 4a. In this instance, the guide elements 14 for the gas stream 15 are arranged in such a wa that an axially infiowing gas flows radially outward in the plane of the ring and, in doing so, flows over the exposed part of the ring. It is possible in accordance with the invention to produce ultra-fine aerosols both of negative and of positive charge with this apparatus.

It is possible by means of the apparatus according to the invention to treat a variety of electrophotographic materials, for example those of the kind described in German patent specification Nos. 1,090,093, 1,046,493, 1,031,127 and 1,052,811. Conventional electrophotographic materials containing zinc oxide dispersed in an insulating vehicle as the photoconductive substance are particularly suitable. The solutions described in German patent specification No. 1,164,829, are suitable for use as developers.

In addition to electrophotographic development, the abovedescribed treatment of the electrophotographic material with the apparatus according to the invention can be used for other purpose, for example, the spraying of dye solutions for sensitising photoconductive layers, or after-treatment of developed layers with solvents for the image dyes, processes which are described in United States patent specification 3,298,830, the corresponding U.K. specification 1,020,831, in the UK. specification 997,272 and Belgian patent specification 681,388.

I claim:

1. An apparatus for the electrostatic atomization of liquids comprising a ring-shaped electrode, rotation means for rotating said electrode whereby electrostatic liquid on the surface of said electrode is atomized, said rotation means including a plurality of guide rollers, said electrode being mounted on said rollers, and drive means for rotating said electrode about an axis perpendicular to the plane of the ring, including a housing, said guide rollers and part of said electrode being mounted in said housing, a liquid supply in said housing, a portion of said electrode passing through said liquid supply, and one of said guide rollers comprising liquid control means for removing excess liquid from said electrode.

2. An apparatus as set forth in claim 1 wherein another of said guide rollers is disposed in said liquid supply.

3. An apparatus for the electrostatic atomization of liquids comprising a ring-shaped electrode, rotation means for rotating said electrode whereby electrostatic liquid on the surface of said electrode is atomized, including guide means for directing a gas stream axially toward the plane of the ring and radially over an exposed portion of said electrode to surround said electrode, and said gas having a dielectric strength higher than air.

4. An apparatus for the electrostatic atomization of liquids comprising a ring-shaped electrode, rotation means for rotating said electrode whereb electrostatic liquid on the surface of said electrode is atomized, said rotation means including a plurality of guide rollers, said electrode being mounted on said rollers, and drive means for rotating said electrode about an axis perpendicular to the plane of the ring, including a housing, said guide rollers and part of said electrode being mounted in said housing, the remainder of said electrode being exposed to the atmosphere, at liquid supply in said housing, the part of said electrode in said housing dipping into said liquid supply with said liquid supply thereby contacting said electrode for feeding liquid from said supply to said electrode.

5. An apparatus as set forth in claim 4 wherein one of said guide rollers dips into said liquid supply.

References Cited UNITED STATES PATENTS 1,545,669 7/1925 Linke 239220 2,777,784 1/1957 Miller ll8626 XR 2,946,516 7/1960 Wagner 118-300 2,970,824 2/1961 Caplow 239-220 XR 3,171,600 3/1965 Eckey 239-220 3,228,608 1/1966 Simm et al. 239-15 FOREIGN PATENTS 853,541 11/1960 Great Britain.

PETER FELDMAN, Primary Examiner. 

